Portfwd - Portfwd Forwarding Daemon

This page last update: 2002/05/05

SourceForge's Project Summary: http://sf.net/projects/portfwd/

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Portfwd's README

# portfwd - Port Forwarding Daemon
# $Id: README,v 1.5 2002/05/05 04:39:42 evertonm Exp $


        Portfwd - Port Forwarding Daemon

        This program is free software; you can redistribute it and/or
        modify it under the terms of the GNU General Public License as
        published by the Free Software Foundation; either version 2 of
        the License, or (at your option) any later version.

        This program is distributed in the hope that it will be
        useful, but WITHOUT ANY WARRANTY; without even the implied
        PURPOSE.  See the GNU General Public License for more details.

        You should have received a copy of the GNU General Public
        License along with this program; if not, write to the Free
        Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,
        MA 02111-1307 USA


        Portfwd stands for port forwarding daemon. It's a small C++
        utility which forwards incoming TCP connections and/or UDP
        packets to remote hosts.

        My apologies for my poor English. Corrections are welcome.


        -- Forwarding of TCP segments.

        -- Forwarding of UDP datagrams.

        -- Forwarding of FTP in active and/or passive modes.

        -- Transparent proxying available under Linux. Portfwd detects
        such facility in "./configure" time by searching the
        definition of MSG_PROXY in .

        -- DNS names for destination hosts can be resolved upon
        start-up or on demand (see "on-the-fly" DNS option).

        -- Portfwd can listen on specific local addresses.

        -- Source addresses for outgoing connections can be explicitly
        specified or automatically selected by the system.

        -- Structured configuration language allows specification of
        multiple simultaneous forwarding processes.

        -- Portfwd spawns one forwarder process for each set of ports
        which are subject to the same rules. Within a process, Portfwd
        uses a select()-based event-loop to concurrently handle
        several network events. There is no threading. There is no
        further process creation after the startup of the configured

        -- The destination of a connection/datagram can be selected
        based on its source address/port pair.

        -- Portfwd allows simple round-robin load-balancing through
        specification of multiple destinations.


        -- Port ranges cannot be forwarded. Ports must be specified in
        a one-by-one basis.

        -- Specification of source address for outgoing UDP datagrams
        require transparent proxy support available in the OS kernel.

        -- The daemon must be restarted in order to update its

        -- A forwarding process blocks on some system calls, such as


        This program has been compiled with gcc 2.95.2 and tested
        under Debian Potato (Linux 2.2.19), but it may work on other
        plataforms as well.

        As of version 0.18, Portfwd has been ported for FreeBSD and
        Solaris and there is support for autoconf/automake.

        In order to compile:


        A file named 'portfwd' should be produced.


        To install 'portfwd' under /usr/local/sbin:

                make install

        Otherwise, just copy 'portfwd' to a suitable location.


        The grammar for the configuration file is described in the
        'conf.txt' file. Examples can be found in the 'cfg' directory.

        For a quick experiment, use the following redirector, then
        test with "telnet 10000". It should give you telnet
        access to your local machine.

         * telnet.cfg
         * Forward all connections on TCP port 10000 to
        tcp { 10000 { => } }
         * eof: telnet.cfg

        Below you can see a more complete example using most features
        of portfwd.

         * example.cfg
        user  nobody
        group nobody
        tcp /* TCP connections */
                 * Connections on port 12000 from subnet localhost/24 and
                 * ports in the range 0-5000 are forwarded to
                 * Anything else goes to localhost:80.
                12000 { 
                        localhost/24:+5000  =>;
                        /* anything else */ => localhost:80
                 * On port 11000, connections from address localhost, any 
                 * port, are forwarded to
                11000 { localhost => };
                { => localhost:ftp }
        udp /* UDP packets */
                 * All packets on port 10000 are forwarded to
                10000 { => }
         * eof: example.cfg


        1. START

        portfwd -c 

        2. STOP

        Send a TERM signal to the Portfwd master process (the one with
        lowest PID).


        Syntax Help

                Option -h provides brief help on command line syntax.

        Running in Foreground

                The -g switch prevents Portfwd from going to

        Configuration File

                Use -c  to specify the location of
                your configuration file.

        On-the-fly DNS

                Portfwd usually solves all DNS hostnames upon
                startup. Specify the -f option if you want the
                destination hostnames be updated on demand. Be aware
                this can affect TCP connection times and the whole UDP
                forwarding performance.

        Transparent Proxy

                The -t switch enables transparent proxying; i.e. IP
                address of outgoing data are "faked" to match those
                from incoming data. If you plan to forward data to
                hosts behind your firewall, you probably want this
                option turned on, as it allows for your servers to see
                original addresses of clients.

                Of course, this feature requires transparent proxy
                support compiled in your kernel.


                If the -d switch is given, portfwd will produce
                verbose logging for debug purposes. Up to 3 switches
                are meaningful.

                Failure messages are sent to the system log under the
                "daemon" facility.

        Program Version

                Portfwd version can be obtained by passing the -v


        If you have further questions, please consult the FAQ.

        There is a discussion board in the Portfwd web site at Source


        This is probably the most useful resource for Portfwd users.

        Anyway, one can contact me directly at:

                Everton da Silva Marques
                evertonsm at yahoo dot com dot br

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